[molpro-user] How to define occ, closed and core n1, n2, n3, n4, n5, n6, n7, n8?

Wenjun Li wli12 at ncsu.edu
Tue May 31 08:27:40 BST 2011

Dear Molpro Users,

I am a very new trial user of Molpro. I found that one key difference
between Molpro and Gaussian is that, Molpro tries to solve the Schrodinger
Equation as accurately as possible using all kinds of great methods to
consider the electron correlation very well, especially using
Multi-Reference Methods and lots of great and new methods developed from the
authors of Molpro, this is great.

However, to use Molpro is also becoming much more complicated than Gaussian,
mainly because of two key reasons: (1) Molpro does not have a very great
interface program for the input and output files editing and showing so far,
certainly Molpro-View is great for this, but it is still not good enough at
all comparing with GaussView, GaussView can almost let user to set up a
calculation very quickly and easily, even though the user does not have a
very good background on quantum chemistry. I heard of that, now Molpro
developers are working on this kinds of interface program for Molpro, which
will be definitely valuable for users. (2) Molpro requires the users to
input lots of very details for solving the electronic structure calculation,
including picking up different methods, options and directives, which really
requires the users to have a very solid background on quantum chemistry, or
else you will not really be able to use Molpro accurately and efficiently,
just like me.

I am one of the users who's background is not in quantum chemistry, I know
very little on molecular symmetry stuff,  and I have only a very weak
quantum chemistry background, which makes me lots of troubles to use Molpro.
One very key difficulty for me so far is that, I can never figure out how to
define *occ, closed and core n1,n2,n3,n4,n5,n6,n7,n8.* For example for *
occ,n1,n2,n3,n4,n5,n6,n7,n8*, ni is the number of occupied orbitals in the
irreducible representation i. This is the only very short description for
OCC in Molpro Manuals, but I can never figure out how to define *occ, closed
and core n1,n2,n3,n4,n5,n6,n7,n8.*

So far what I understood is like that, *n1 is the # of sigma orbitals, **n2
is the # of sigma* orbitals, **n3 is the # of pi-x orbitals, **n4 is the #
of pi-x* orbitals, **n5 is the # of pi-y orbitals, **n6 is the # of pi-y*
orbitals,* *then what is n7 and n8?* Am I right? Most likely I am wrong, I
am actually always confused about how to Define the number of occupied
orbitals in each symmetry. I believe this is most likely due to my weak
quantum chemistry background. So may I ask for some suggestions from the
Molpro-users. How can I define *occ, closed and core
n1,n2,n3,n4,n5,n6,n7,n8.*? Where can I find some more references or
descriptions for this? Or maybe can some one suggest me to read some kinds
of textbook, so that I can understand this background info.

Thanks a lot for all the help and suggestions in advance. Sorry for the long
email, but maybe I did say something for very new users, who does not have a
solid quantum chemistry background. Thanks a lot again.

Best regards,

*Wenjun LI *
Chemical & Biomolecular Engineering,
North Carolina State University,
Engineering Building I, Box 7905,
911 Partners Way, Raleigh, NC 27695
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